HESI A2 Anatomy and Physiology Quizlet

Correct Answer: A

Rationale: The correct answer is A: Melatonin. Melatonin is a hormone produced by the pineal gland that plays a key role in regulating the sleep-wake cycle. It helps control the body's internal clock and signals the brain when it's time to sleep. Melatonin levels typically rise in the evening, promoting sleep, and decrease in the morning, promoting wakefulness. Summary of incorrect choices: B: Insulin - Insulin is a hormone that regulates blood sugar levels, not the sleep-wake cycle. C: Cortisol - Cortisol is a stress hormone that helps regulate metabolism and immune response, but it does not directly control the sleep-wake cycle. D: Thyroxine - Thyroxine is a hormone produced by the thyroid gland that regulates metabolism, growth, and development, but it is not directly involved in the sleep-wake cycle regulation.

Correct Answer: B

Rationale: The correct answer is B: Vitamin K. Vitamin K is essential for blood clotting as it helps in the production of proteins necessary for the clotting process. Deficiency in Vitamin K can lead to excessive bleeding. A: Vitamin A is important for vision and immune function, not blood clotting. C: Vitamin C is important for collagen synthesis and immune function, not blood clotting. D: Vitamin D is important for calcium absorption and bone health, not blood clotting.

Correct Answer: C

Rationale: The correct answer is C: Pineal gland. The pineal gland secretes melatonin, a hormone responsible for regulating sleep-wake cycles. It receives signals from the retina about light levels, which helps to synchronize the body's internal clock. The hypothalamus (A) regulates various bodily functions but is not specifically responsible for sleep-wake cycles. The thalamus (B) is involved in relaying sensory information but not directly related to sleep regulation. The cerebellum (D) is primarily involved in motor control and coordination, not sleep regulation. Therefore, the pineal gland is the structure in the brain that directly regulates sleep and wakefulness.

Correct Answer: A

Rationale: The main function of the circulatory system is to transport oxygen and nutrients to all cells in the body. This is achieved through the blood vessels and the pumping action of the heart. Oxygen is necessary for cellular respiration, while nutrients are essential for cell growth and metabolism. Without these, cells cannot function properly, leading to organ failure and ultimately, death. Options B, C, and D are incorrect because although the circulatory system indirectly helps remove waste products, regulate body temperature, and protect organs, these are not its primary functions.

Correct Answer: B

Rationale: The correct answer is B: Mitochondria. Mitochondria are known as the powerhouse of the cell because they are responsible for energy production through the process of cellular respiration. They produce ATP, the main energy currency of the cell. The other choices are incorrect because the nucleus is responsible for storing genetic material, ribosomes are involved in protein synthesis, and the Golgi apparatus is responsible for packaging and transporting proteins. Therefore, only the mitochondria play a direct role in energy production within the cell.